Installed a 518OD in my Cuda last winter. Rebuilt it with good parts and advice here and on other sites. It works good but I have noticed an odd phenomenon. It has a vibration in high gear. Not in low, second or OD, just in high. It is not RPM related, although it is more pronounced as RPM rises.

I have over 1,000 miles on this tranny now. The vibration is not great, but is noticeable to the point of annoyance.

I have asked around here locally and no one has ever heard of a high gear vibration on our automatics. A couple of guys have told me it wasn't possible to have a vibration in high only.

So, I guess my question is, has anyone ever experienced a vibration in high gear in a 727/518? Is it safe to assume that the only possible explanation is a problem with that drum.

Just my luck to have a weird thing like this pop up after it is all together and working good.

Thanks!

how does it act in overdrive ? is the vibration still there only worse, or no vibration in overdrive ?

I am thinking it's not the trans as every thing that is applied in 3rd in the 3 speed section of the trans is also applied in O/D. It is probably related to drive shaft speed or engine RPM.

Did you reuse your original driveshaft or did the use of the 518 require a new driveshaft? If a new driveshaft with a different length was needed were you able to maintain the optimal u-joint angles?

my 518 does the same thing, it does not do it all the time, when it does do it I switch into OD & it stops, I think that my builder did not mark,index all of the overdrive parts like the rebuild manual says to do.I have read that if the OD drums & parts are not put back indexed the same way they came apart they can cause a vibration.

So, you think the issue may be in the OD unit and not the high speed drum? I couldn't imagine anything but a drum causing the vibration, but I didn't know for sure.

Does that mean that I may be able to tackle the problem by pulling the tail shaft to access the OD unit rather than pulling the trans? And like yours, mine seems to vibrate sometimes more than others. Sometimes it's annoying and other times I hardly notice it.

As to all the other questions; it is not RPM related because 2nd and OD do not vibrate like 3rd at any given RPM. It is not speed related because I can shift out of second with no vibration and get the vibration when it goes into 3rd and loose the vibration when I go into OD all while maintaining the same speed.

And yes, I had to have my driveshaft cut. It won't even go in when changing to the 518 if you don't. It's just too long. The drive train angles are not perfect, they never are on my stuff. But in using the Tremec app, they are very close. And I have played around with them to see what would happen. Again, I have put over 1,000 miles on this combo and have experimented around with it because I just couldn't believe that I had a 3rd gear vibration due to the tranny. But I think I have eliminated most other possibilities.

On mine it is not drive line angle, or engine or anything else but the trans,I can go 35 mph in third gear,vibration present,engage & disengage the OD keeping the same 35 mph & the vibration goes away.

Interesting, I have a low speed shudder in 2 and 3rd, goes away at higher speed and doesn't happen in OD.

It could still be RPM related. Think of it this way, in 3rd gear certain components in the main case are turning at a certain RPM but when OD is engaged those same components slow down when maintaining the same road speed as before the OD was engaged.

Okay............. I think. What about the 2nd and 3rd vibration difference?

So, where do you think my problem lies, John?

How's your pinion angle? Have you tried turning the driveshaft 180* in the rear end yoke?